diff --git a/documentation/RELEASE_NOTES.html b/documentation/RELEASE_NOTES.html
index 2a91b73c0..d90a5847a 100644
--- a/documentation/RELEASE_NOTES.html
+++ b/documentation/RELEASE_NOTES.html
@@ -20,6 +20,28 @@
 
 -->
 
+<h3>epicsTime API return status</h3>
+
+<p>The epicsTime routines that used to return epicsTimeERROR now return a specific
+S_time_ status value, allowing the caller to discover the reason for any failure.
+The identifier <tt>epicsTimeERROR</tt> is no longer defined, so any references to
+it in source code will no longer compile. The identifier epicsTimeOK still exists
+and has the value 0 as before, so most code that uses these APIs can be changed in
+a way that is backwards-compatible with the previous return status.</p>
+
+<p>Time providers that have to return a status value and still need to be built
+with earlier versions of Base can define the necessary status symbols like this:</p>
+
+<blockquote><pre>
+#include "epicsTime.h"
+
+#ifndef M_time
+/* S_time_... status values were not provided before Base 3.16 */
+#define S_time_unsynchronized epicsTimeERROR
+#define S_time_...whatever... epicsTimeERROR
+#endif
+</pre></blockquote>
+
 <h3>Refactoring of epicsReadline</h3>
 
 <p>The epicsReadline code has been reorganized to allow the commandline history
diff --git a/src/libCom/error/Makefile b/src/libCom/error/Makefile
index bf81074e8..0a99b0def 100644
--- a/src/libCom/error/Makefile
+++ b/src/libCom/error/Makefile
@@ -22,6 +22,7 @@ Com_SRCS += errSymTbl.c
 # For bldErrSymTbl
 #
 ERR_S_FILES += $(LIBCOM)/osi/devLib.h
+ERR_S_FILES += $(LIBCOM)/osi/epicsTime.h
 ERR_S_FILES += $(LIBCOM)/as/asLib.h
 ERR_S_FILES += $(LIBCOM)/misc/epicsStdlib.h
 ERR_S_FILES += $(LIBCOM)/pool/epicsThreadPool.h
diff --git a/src/libCom/error/errMdef.h b/src/libCom/error/errMdef.h
index 27b693d8c..e511d912b 100644
--- a/src/libCom/error/errMdef.h
+++ b/src/libCom/error/errMdef.h
@@ -50,6 +50,7 @@ extern "C" {
 #define M_gddFuncTbl	(526 <<16) /*gdd jump table*/
 #define M_stdlib        (527 <<16) /*EPICS Standard library*/
 #define M_pool          (528 <<16) /*Thread pool*/
+#define M_time          (529 <<16) /*epicsTime*/
 
 epicsShareFunc void epicsShareAPI errSymLookup(long status, char *pBuf, unsigned bufLength);
 epicsShareFunc void epicsShareAPI errSymTest(unsigned short modnum, unsigned short begErrNum, unsigned short endErrNum);
diff --git a/src/libCom/osi/epicsGeneralTime.c b/src/libCom/osi/epicsGeneralTime.c
index 8ef8a73cc..7f8e1b66f 100644
--- a/src/libCom/osi/epicsGeneralTime.c
+++ b/src/libCom/osi/epicsGeneralTime.c
@@ -86,7 +86,7 @@ void generalTime_Init(void)
 int generalTimeGetExceptPriority(epicsTimeStamp *pDest, int *pPrio, int ignore)
 {
     gtProvider *ptp;
-    int status = epicsTimeERROR;
+    int status = S_time_noProvider;
 
     generalTime_Init();
 
@@ -107,6 +107,7 @@ int generalTimeGetExceptPriority(epicsTimeStamp *pDest, int *pPrio, int ignore)
                     *pPrio = ptp->priority;
             } else {
                 int key;
+
                 *pDest = gtPvt.lastProvidedTime;
                 if (pPrio)
                     *pPrio = gtPvt.lastTimeProvider->priority;
@@ -117,8 +118,7 @@ int generalTimeGetExceptPriority(epicsTimeStamp *pDest, int *pPrio, int ignore)
             break;
         }
     }
-    if (status == epicsTimeERROR &&
-        ignore == 0)
+    if (status && ignore == 0)
         gtPvt.lastTimeProvider = NULL;
     epicsMutexUnlock(gtPvt.timeListLock);
 
@@ -135,7 +135,8 @@ int epicsTimeGetCurrentInt(epicsTimeStamp *pDest)
     gtProvider *ptp = gtPvt.lastTimeProvider;
 
     if (ptp == NULL ||
-        ptp->getInt.Time == NULL) return epicsTimeERROR;
+        ptp->getInt.Time == NULL)
+	return S_time_noProvider;
 
     return ptp->getInt.Time(pDest);
 }
@@ -145,20 +146,20 @@ static int generalTimeGetEventPriority(epicsTimeStamp *pDest, int eventNumber,
     int *pPrio)
 {
     gtProvider *ptp;
-    int status = epicsTimeERROR;
+    int status = S_time_noProvider;
 
     generalTime_Init();
 
     if ((eventNumber < 0 || eventNumber >= NUM_TIME_EVENTS) &&
         (eventNumber != epicsTimeEventBestTime))
-        return status;
+        return S_time_badEvent;
 
     epicsMutexMustLock(gtPvt.eventListLock);
     for (ptp = (gtProvider *)ellFirst(&gtPvt.eventProviders);
          ptp; ptp = (gtProvider *)ellNext(&ptp->node)) {
 
         status = ptp->get.Event(pDest, eventNumber);
-        if (status != epicsTimeERROR) {
+        if (status == epicsTimeOK) {
             gtPvt.lastEventProvider = ptp;
             if (pPrio)
                 *pPrio = ptp->priority;
@@ -169,6 +170,7 @@ static int generalTimeGetEventPriority(epicsTimeStamp *pDest, int eventNumber,
                     gtPvt.lastProvidedBestTime = *pDest;
                 } else {
                     int key;
+
                     *pDest = gtPvt.lastProvidedBestTime;
                     key = epicsInterruptLock();
                     gtPvt.ErrorCounts++;
@@ -180,6 +182,7 @@ static int generalTimeGetEventPriority(epicsTimeStamp *pDest, int eventNumber,
                     gtPvt.eventTime[eventNumber] = *pDest;
                 } else {
                     int key;
+
                     *pDest = gtPvt.eventTime[eventNumber];
                     key = epicsInterruptLock();
                     gtPvt.ErrorCounts++;
@@ -189,7 +192,7 @@ static int generalTimeGetEventPriority(epicsTimeStamp *pDest, int eventNumber,
             break;
         }
     }
-    if (status == epicsTimeERROR)
+    if (status)
         gtPvt.lastEventProvider = NULL;
     epicsMutexUnlock(gtPvt.eventListLock);
 
@@ -213,7 +216,8 @@ int epicsTimeGetEventInt(epicsTimeStamp *pDest, int eventNumber)
         gtProvider *ptp = gtPvt.lastEventProvider;
 
         if (ptp == NULL ||
-            ptp->getInt.Event == NULL) return epicsTimeERROR;
+            ptp->getInt.Event == NULL)
+	    return S_time_noProvider;
 
         return ptp->getInt.Event(pDest, eventNumber);
     }
@@ -271,11 +275,11 @@ int generalTimeRegisterEventProvider(const char *name, int priority,
     generalTime_Init();
 
     if (name == NULL || getEvent == NULL)
-        return epicsTimeERROR;
+        return S_time_badArgs;
 
     ptp = (gtProvider *)malloc(sizeof(gtProvider));
     if (ptp == NULL)
-        return epicsTimeERROR;
+        return S_time_noMemory;
 
     ptp->name         = epicsStrDup(name);
     ptp->priority     = priority;
@@ -293,7 +297,7 @@ int generalTimeAddIntEventProvider(const char *name, int priority,
     gtProvider *ptp = findProvider(&gtPvt.eventProviders, gtPvt.eventListLock,
         name, priority);
     if (ptp == NULL)
-        return epicsTimeERROR;
+        return S_time_noProvider;
 
     ptp->getInt.Event = getEvent;
 
@@ -308,11 +312,11 @@ int generalTimeRegisterCurrentProvider(const char *name, int priority,
     generalTime_Init();
 
     if (name == NULL || getTime == NULL)
-        return epicsTimeERROR;
+        return S_time_badArgs;
 
     ptp = (gtProvider *)malloc(sizeof(gtProvider));
     if (ptp == NULL)
-        return epicsTimeERROR;
+        return S_time_noMemory;
 
     ptp->name        = epicsStrDup(name);
     ptp->priority    = priority;
@@ -330,7 +334,7 @@ int generalTimeAddIntCurrentProvider(const char *name, int priority,
     gtProvider *ptp = findProvider(&gtPvt.timeProviders, gtPvt.timeListLock,
         name, priority);
     if (ptp == NULL)
-        return epicsTimeERROR;
+        return S_time_noProvider;
 
     ptp->getInt.Time = getTime;
 
@@ -388,7 +392,7 @@ long generalTimeReport(int level)
         if (!message) {
             epicsMutexUnlock(gtPvt.timeListLock);
             printf("Out of memory\n");
-            return epicsTimeERROR;
+            return S_time_noMemory;
         }
 
         pout = message;
@@ -399,7 +403,7 @@ long generalTimeReport(int level)
                 ptp->name, ptp->priority);
             if (level) {
                 epicsTimeStamp tempTS;
-                if (ptp->get.Time(&tempTS) != epicsTimeERROR) {
+                if (ptp->get.Time(&tempTS) == epicsTimeOK) {
                     char tempTSText[40];
                     epicsTimeToStrftime(tempTSText, sizeof(tempTSText),
                         "%Y-%m-%d %H:%M:%S.%06f", &tempTS);
@@ -430,7 +434,7 @@ long generalTimeReport(int level)
         if (!message) {
             epicsMutexUnlock(gtPvt.eventListLock);
             printf("Out of memory\n");
-            return epicsTimeERROR;
+            return S_time_noMemory;
         }
 
         pout = message;
diff --git a/src/libCom/osi/epicsTime.cpp b/src/libCom/osi/epicsTime.cpp
index b85b67b8e..59514c2f7 100644
--- a/src/libCom/osi/epicsTime.cpp
+++ b/src/libCom/osi/epicsTime.cpp
@@ -284,7 +284,7 @@ epicsTime::operator local_tm_nano_sec () const
     local_tm_nano_sec tm;
 
     int status = epicsTime_localtime ( &ansiTimeTicks.ts, &tm.ansi_tm );
-    if ( status != epicsTimeOK ) {
+    if ( status ) {
         throw std::logic_error ( "epicsTime_localtime failed" );
     }
 
@@ -303,7 +303,7 @@ epicsTime::operator gm_tm_nano_sec () const
     gm_tm_nano_sec tm;
 
     int status = epicsTime_gmtime ( &ansiTimeTicks.ts, &tm.ansi_tm );
-    if ( status != epicsTimeOK ) {
+    if ( status ) {
         throw std::logic_error ( "epicsTime_gmtime failed" );
     }
 
@@ -891,7 +891,7 @@ extern "C" {
             *pDest = dst.ts;
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -903,7 +903,7 @@ extern "C" {
             *pDest = epicsTime ( dst );
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -915,7 +915,7 @@ extern "C" {
             *pNSecDest = tmns.nSec;
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -927,7 +927,7 @@ extern "C" {
             *pNSecDest = gmtmns.nSec;
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -940,7 +940,7 @@ extern "C" {
             *pDest = epicsTime (tmns);
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -950,7 +950,7 @@ extern "C" {
             *pDest = epicsTime (*pSrc);
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -960,7 +960,7 @@ extern "C" {
             *pDest = epicsTime (*pSrc);
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -970,7 +970,7 @@ extern "C" {
             *pDest = epicsTime (*pSrc);
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
@@ -980,7 +980,7 @@ extern "C" {
             *pDest = epicsTime (*pSrc);
         }
         catch (...) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         return epicsTimeOK;
     }
diff --git a/src/libCom/osi/epicsTime.h b/src/libCom/osi/epicsTime.h
index a36d6afe3..bf8f77c87 100644
--- a/src/libCom/osi/epicsTime.h
+++ b/src/libCom/osi/epicsTime.h
@@ -17,6 +17,7 @@
 #include "shareLib.h"
 #include "epicsTypes.h"
 #include "osdTime.h"
+#include "errMdef.h"
 
 /* The EPICS Epoch is 00:00:00 Jan 1, 1990 UTC */
 #define POSIX_TIME_AT_EPICS_EPOCH 631152000u
@@ -170,9 +171,15 @@ private:
 extern "C" {
 #endif /* __cplusplus */
 
-/* All epicsTime routines return (-1,0) for (failure,success) */
+/* epicsTime routines return S_time_ error status values */
 #define epicsTimeOK 0
-#define epicsTimeERROR (-1)
+#define S_time_noProvider       (M_time| 1) /*No time provider*/
+#define S_time_badEvent         (M_time| 2) /*Bad event number*/
+#define S_time_badArgs          (M_time| 3) /*Invalid arguments*/
+#define S_time_noMemory         (M_time| 4) /*Out of memory*/
+#define S_time_unsynchronized   (M_time| 5) /*Provider not synchronized*/
+#define S_time_timezone         (M_time| 6) /*Invalid timeone*/
+#define S_time_conversion       (M_time| 7) /*Time conversion error*/
 
 /*Some special values for eventNumber*/
 #define epicsTimeEventCurrentTime 0
diff --git a/src/libCom/osi/os/Darwin/osdTime.cpp b/src/libCom/osi/os/Darwin/osdTime.cpp
index f3e6db5dd..c4a7e838c 100644
--- a/src/libCom/osi/os/Darwin/osdTime.cpp
+++ b/src/libCom/osi/os/Darwin/osdTime.cpp
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
 #include <mach/mach.h>
 #include <mach/clock.h>
 
@@ -52,13 +53,13 @@ static int done = timeRegister();
 int epicsTime_gmtime(const time_t *pAnsiTime, struct tm *pTM)
 {
     return gmtime_r(pAnsiTime, pTM) ?
-        epicsTimeOK : epicsTimeERROR;
+        epicsTimeOK : errno;
 }
 
 int epicsTime_localtime(const time_t *clock, struct tm *result)
 {
     return localtime_r(clock, result) ?
-        epicsTimeOK : epicsTimeERROR;
+        epicsTimeOK : errno;
 }
 
 extern "C" epicsShareFunc void
diff --git a/src/libCom/osi/os/RTEMS/osdTime.cpp b/src/libCom/osi/os/RTEMS/osdTime.cpp
index acefa1b09..b233ec1e5 100644
--- a/src/libCom/osi/os/RTEMS/osdTime.cpp
+++ b/src/libCom/osi/os/RTEMS/osdTime.cpp
@@ -91,7 +91,7 @@ int epicsTime_gmtime ( const time_t *pAnsiTime, struct tm *pTM )
         return epicsTimeOK;
     }
     else {
-        return epicsTimeERROR;
+        return errno;
     }
 }
 
@@ -102,7 +102,7 @@ int epicsTime_localtime ( const time_t *clock, struct tm *result )
         return epicsTimeOK;
     }
     else {
-        return epicsTimeERROR;
+        return errno;
     }
 }
 
diff --git a/src/libCom/osi/os/WIN32/osdTime.cpp b/src/libCom/osi/os/WIN32/osdTime.cpp
index 67b127200..d43a6aa44 100644
--- a/src/libCom/osi/os/WIN32/osdTime.cpp
+++ b/src/libCom/osi/os/WIN32/osdTime.cpp
@@ -164,7 +164,7 @@ int epicsShareAPI epicsTime_gmtime ( const time_t *pAnsiTime, struct tm *pTM )
     SYSTEMTIME st;
     BOOL status = FileTimeToSystemTime ( &ft, &st );
     if ( ! status ) {
-        return epicsTimeERROR;
+        return S_time_conversion;
     }
 
     pTM->tm_sec = st.wSecond; // seconds after the minute - [0,59]
@@ -193,7 +193,7 @@ int epicsShareAPI epicsTime_localtime (
     TIME_ZONE_INFORMATION tzInfo;
     DWORD tzStatus = GetTimeZoneInformation ( & tzInfo );
     if ( tzStatus == TIME_ZONE_ID_INVALID ) {
-        return epicsTimeERROR;
+        return S_time_timezone;
     }
 
     //
@@ -204,13 +204,13 @@ int epicsShareAPI epicsTime_localtime (
     SYSTEMTIME st;
     BOOL success = FileTimeToSystemTime ( & ft, & st );
     if ( ! success ) {
-        return epicsTimeERROR;
+        return S_time_conversion;
     }
     SYSTEMTIME lst;
     success = SystemTimeToTzSpecificLocalTime (
         & tzInfo, & st, & lst );
     if ( ! success ) {
-        return epicsTimeERROR;
+        return S_time_conversion;
     }
 
     //
@@ -220,7 +220,7 @@ int epicsShareAPI epicsTime_localtime (
     FILETIME lft;
     success = SystemTimeToFileTime ( & lst, & lft );
     if ( ! success ) {
-        return epicsTimeERROR;
+        return S_time_conversion;
     }
 
     int is_dst = -1; // unknown state of dst
@@ -234,14 +234,14 @@ int epicsShareAPI epicsTime_localtime (
         success = SystemTimeToFileTime (
             & tzInfo.StandardDate, & StandardDateFT );
         if ( ! success ) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         tzInfo.DaylightDate.wYear = st.wYear;
         FILETIME DaylightDateFT;
         success = SystemTimeToFileTime (
             & tzInfo.DaylightDate, & DaylightDateFT );
         if ( ! success ) {
-            return epicsTimeERROR;
+            return S_time_conversion;
         }
         if ( CompareFileTime ( & lft, & DaylightDateFT ) >= 0
                 && CompareFileTime ( & lft, & StandardDateFT ) < 0 ) {
diff --git a/src/libCom/osi/os/posix/osdTime.cpp b/src/libCom/osi/os/posix/osdTime.cpp
index 679c6e376..7713a2c25 100644
--- a/src/libCom/osi/os/posix/osdTime.cpp
+++ b/src/libCom/osi/os/posix/osdTime.cpp
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
 
 #include "osiSock.h"
 
@@ -36,7 +37,7 @@
         struct timezone tz;
 
         if (gettimeofday (&tv, &tz))
-            return epicsTimeERROR;
+            return errno;
 
         *pDest = epicsTime(tv);
         return epicsTimeOK;
@@ -68,7 +69,7 @@ int epicsTime_gmtime ( const time_t *pAnsiTime,
         return epicsTimeOK;
     }
     else {
-        return epicsTimeERROR;
+        return errno;
     }
 }
 
@@ -80,7 +81,7 @@ int epicsTime_localtime ( const time_t *clock,
         return epicsTimeOK;
     }
     else {
-        return epicsTimeERROR;
+        return errno;
     }
 }
 
diff --git a/src/libCom/osi/osiNTPTime.c b/src/libCom/osi/osiNTPTime.c
index 64362b2e8..d22df861b 100644
--- a/src/libCom/osi/osiNTPTime.c
+++ b/src/libCom/osi/osiNTPTime.c
@@ -164,7 +164,7 @@ static void NTPTimeSync(void *dummy)
         }
 
         if (timespecNow.tv_sec <= POSIX_TIME_AT_EPICS_EPOCH ||
-            epicsTimeFromTimespec(&timeNow, &timespecNow) == epicsTimeERROR) {
+            epicsTimeFromTimespec(&timeNow, &timespecNow) != epicsTimeOK) {
             errlogPrintf("NTPTimeSync: Bad time received from NTP server\n");
             NTPTimePvt.synchronized = 0;
             continue;
@@ -213,7 +213,7 @@ static int NTPTimeGetCurrent(epicsTimeStamp *pDest)
     epicsUInt32 ticksSince;
 
     if (!NTPTimePvt.synchronized)
-        return epicsTimeERROR;
+        return S_time_unsynchronized;
 
     epicsMutexMustLock(NTPTimePvt.lock);
 
diff --git a/src/std/dev/devGeneralTime.c b/src/std/dev/devGeneralTime.c
index c656c85db..0cce00d4b 100644
--- a/src/std/dev/devGeneralTime.c
+++ b/src/std/dev/devGeneralTime.c
@@ -37,7 +37,7 @@ static int getCurrentTime(double * pseconds)
 {
     epicsTimeStamp ts;
 
-    if (epicsTimeERROR != epicsTimeGetCurrent(&ts)) {
+    if (epicsTimeOK == epicsTimeGetCurrent(&ts)) {
         *pseconds = ts.secPastEpoch + ((double)(ts.nsec)) * 1e-9;
         return 0;
     }